1. Field of the Invention
The present invention relates to a wafer bake apparatus.
2. Description of the Related Art
In general, a wafer bake apparatus is used to volatilize the solvent of a photoresist coating on a wafer.
Semiconductor fabrication is largely divided into cleaning, heat treatment, impurity implantation, thin film formation, lithography, and planarization processes. Particularly, the lithography process consists of many steps: exposing a pattern, developing, etching, and photoresist removing. As for the exposing a pattern, a desired pattern on a mask substrate or reticle is projected onto the surface of a wafer at a reduction ratio. In fact, this process is a vital technique of all the processes and requires the most expensive equipment available. Once the pattern is formed, an etching process is performed using the photoresist pattern as a mask.
Before coating the photoresist for forming a pattern on the wafer, the surface of the wafer should be dry. In order to remove water (moisture) from the surface of the wafer, the wafer is usually heated at a predetermined temperature. FIG. 1 is a schematic view of a related art wafer bake apparatus for heating a wafer at a predetermined temperature.
As shown in FIG. 1, the wafer bake apparatus includes a process chamber 1, a hot plate 2, and a wafer lift unit 3 for moving a wafer W to a baking position and an unloading position. The wafer W is placed on a plurality of proximities 4 disposed on the hot plate 2. The process chamber 1 has a cover 5, and the wafer lift unit 3 has lift pins 3a to be inserted into a plurality of through holes 2a that are formed in the hot plate 2.
In the wafer bake apparatus, the wafer W is usually lifted by a robot (not shown) onto the lift pins 3a protruded upwards from the hot plate 2. Then, as the wafer lift unit 3 descends the wafer W is placed on the baking position, i.e., on the proximities 4 of the hot plate 2, to be baked (please refer to FIG. 2).
When the baking is complete the wafer W is moved to the unloading position as shown in FIG. 3 by means of the lift pins 3a which ascend by the wafer lift unit 3. Then the robot (not shown) unloads the wafer W from the unloading position.
However, the related art wafer bake apparatus has defects. For instance, as the size of the wafer increases and the separation distance (or gap) between the hot plate 2 and the wafer W is maintained less than 100 μm, air resistance from outside negatively affects the wafer delivery performance by the wafer lift unit 3. As a result, the wafer W is not properly carried and is often damaged.
As FIG. 2 illustrates, sometimes the wafer W is not properly placed at the baking position due to the air resistance between the hot plate 2 and the wafer W. Also, as FIG. 3 illustrates, when the baked wafer W is moved to the unloading position the wafer W can be distorted due to air resistance above the wafer W.